Written by Michael Larabel
Ubuntu 12.10 will not be shipping with a Wayland-based system compositor as was once hoped for, but the experimental system compositor can be enabled from a PPA in a very primitive state.

For the past few weeks there's been the Ubuntu Desktop System Compositor based upon Wayland and Weston that's been available via a PPA (Launchpad Personal Package Archive). The Ubuntu Blueprint for the desktop-q-system-compositor was marked as a high priority item for this next Ubuntu release due out in October, but it's not going to make the cut. Added to the blueprint's whiteboard this week was "seb128, 2012-08-06: descoping the compositor work from quantal, good progresses have been made but it doesn't seem realistic to enable it by default, we will revisit that next cycle." So the system compositor isn't happening for Ubuntu 12.10 and then presumably in Copenhagen it will be discussed whether this is a feasible goal for Ubuntu 13.04 in April.

The focus of this system compositor work was to have a compositor for Ubuntu 12.10 that controlled all video/outputs from boot to shutdown. This work would allow for smooth transitions from start-up to the greeter and back-again, provide a cleaner means of VT switching, offer a consistent monitor layout for all stages of the boot process, using the greeter as the lock screen and ensuring the user can never accidentally switch to a locked session, and for being able to show the greeter while the session loads. The Ubuntu System Compositor is being built atop Wayland with the reference Weston compositor. As recently as last month they were still hoping for the compositor and to have it in the forthcoming Ubuntu 12.10 Beta.

Going back to UDS Oakland when they came up with the ambitious Wayland plans, I saw this as being very unlikely for Ubuntu 12.10. "As someone that's been monitoring Wayland for the past five years and the first person to publicly write about Wayland when it was still a very young and experimental project by Kristian, I just don't see this system compositor goal coming close to fruition with Ubuntu 12.10. I've been saying for a while now that it will probably not be until Ubuntu 13.04 that Wayland takes on any really usable form...If a miracle happens and they hit this system compositor goal for Ubuntu 12.10, they will still maintain the current X.Org experience for those with unsupported hardware / drivers -- namely the proprietary AMD and NVIDIA graphics drivers. Canonical also hopes to convince NVIDIA and AMD to support Wayland by writing a special back-end for their drivers."

Their UDS plans also caused early controversy as originally they wanted to fork Wayland's Weston rather than implement the extended functionality they desired via plug-ins. But at least this Wayland upbringing within the Ubuntu world has led to some rare Wayland-related contributions by Canonical.

Among the remaining work items that were planned for this system compositor initiative but have yet to be tackled include work in the area of VT switching, using the greeter as the lock screen, an X Server signal hook to fake VT switches for input drivers, patching XWayland to use regular input DDX drivers, talking with QA about testing, and writing a Wayland-Plymouth back-end for the start-up/shut-down splash screen. The current Weston within the PPA is also based upon v0.89 -- far from the current upstream Wayland/Weston v0.95.

The plans at this point for the system compositor arenï¿½t to run software natively atop Wayland but rather to use XWayland to have an X.Org Server atop the compositor until all major software is Wayland-compatible. Let's see if this Ubuntu System Compositor will become a reality for Ubuntu 13.04 in April of 2013. Upstream Wayland/Weston meanwhile should be hitting version 1.0 later in the calendar year.

Wayland provides a method for compositing window managers to communicate directly with applications and video hardware and expects them to communicate with input hardware using other libraries. Applications render graphics to their own buffers, and the window manager becomes the display server, compositing those buffers to form the on-screen display of application windows. This is a simpler and more efficient approach than using a compositing window manager with the X Window System.